How to Save Your iPhone SHSH Blobs Using TSS Saver

These are instructions on how to save your iPhone's SHSH blobs using TSS Saver by 1Conan. Your SHSH blobs may help you downgrade or upgrade to a jailbreakable firmware version that is no longer being signed by Apple.

Word of caution before trying futurerestore: the SEP for both, the iOS you're going to downgrade to, and the one currently signed need to have the same SEP (Secure Enclave Processor) OS version.
If they aren't and you go on ahead with the downgrade, either Touch ID or Face ID won't work anymore - can only get fixed with a full .ipsw image restore via iTunes.